Optimization for vertical stabilizers on flutter stability of streamlined box girders with mountainous environment

Wind environment in mountainous areas is very different from that in coastal and plain areas. Strong winds always show large angles of attack, affecting the flutter stability of long-span bridges which is one of the most important design factors. The central vertical stabilizer has been demonstrated to be an effective aerodynamic measure to improve the flutter stability, and this article optimizes the stabilizer to improve its applicability in mountainous areas. Computational fluid dynamics simulations are first performed to analyze the effects of stabilizers with different positions and forms on the flutter stability of an ideal box girder, and the aerodynamic mechanism is discussed based on the static and the dynamic flow fields, respectively. Wind tunnel tests are then carried out to test the critical flutter wind speed of a real box girder equipped with different stabilizers, and the change in its flutter stability is further analyzed. The results show that the vertical stabilizer with appropriate positions and heights can improve the participation level of structural heaving vibration, and thereby increases the flutter stability. At large angles of attack, the big vortex on the leading edge which may drive the bridge to flutter instability is gradually weakened with the increase in stabilizer’s height. Compared with a single stabilizer, double vertical stabilizers, in the midst of which exists a negative pressure region, could achieve better effects.

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Effects of guardrails on wind environment for vehicles and aerodynamic stability for bridges with box girders

Advances in Structural Engineering ◽

10.1177/1369433220956827 ◽

2020 ◽

pp. 136943322095682

Author(s):

Junjie Guo ◽

Haojun Tang ◽

Yongle Li ◽

Zewen Wang

Keyword(s):

Flow Field ◽

Suspension Bridge ◽

Mountainous Areas ◽

Box Girders ◽

Aerodynamic Stability ◽

Wind Environment ◽

Long Span Bridges ◽

Long Span ◽

Strong Winds ◽

Extreme Winds

Normally strong winds in mountainous areas possess potential threats to the safety of vehicles travelling over the long-span bridges. Generally, decreasing the porosity of the guardrails could improve wind environment for vehicles, while the changed flow field around the bridge’s girder may weaken the structural aerodynamic stability simultaneously. To solve the two seemingly contradictory issues, such a long-span suspension bridge in mountainous areas is taken as the case study, and the guardrails are optimized with different schemes. The effects on wind environment for vehicles under normal traffic conditions are first studied by computational fluid dynamics (CFD) simulations. The further effects on the aerodynamic stability of the bridge under extreme winds are then determined by wind tunnel tests, and the observed non-divergent flutter is explainedbythe change in dynamic flow field. Results show that reducing the porosity of guardrails does improve the wind environment above the bridge deck, and the improvement on wind environment increases with the increase in angle of attack. After closing the guardrails completely, however, the girder appears non-divergent vibration different from the linear theoretical flutter when the critical wind speed is exceeded. The different post-flutter behaviors at different angles of attack are mainly related to the synchronization condition between the movement of vortex and the motion of the girder.

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Contributions of Tip Leakage and Inlet Diffusion on Inducer Backflow

Journal of Fluids Engineering ◽

10.1115/1.4043770 ◽

2019 ◽

Vol 141 (12) ◽

Cited By ~ 1

Author(s):

D. Tate Fanning ◽

Steven E. Gorrell ◽

Daniel Maynes ◽

Kerry Oliphant

Keyword(s):

Leading Edge ◽

Tip Clearance ◽

Tip Vortex ◽

Low Flow ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Flow Recirculation ◽

Computational Fluid Dynamics Simulations ◽

Dynamics Simulations

Inducers are used as a first stage in pumps to minimize cavitation and allow the pump to operate at lower inlet head conditions. Inlet flow recirculation or backflow in the inducer occurs at low flow conditions and can lead to instabilities and cavitation-induced head breakdown. Backflow of an inducer with a tip clearance (TC) of τ = 0.32% and with no tip clearance (NTC) is examined with a series of computational fluid dynamics simulations. Removing the TC eliminates tip leakage flow; however, backflow is still observed. In fact, the NTC case showed a 37% increase in the length of the upstream backflow penetration. Tip leakage flow does instigate a smaller secondary leading edge tip vortex that is separate from the much larger backflow structure. A comprehensive analysis of these simulations suggests that blade inlet diffusion, not tip leakage flow, is the fundamental mechanism leading to the formation of backflow.

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A Comparison of Experimental and Computational Heat Transfer Results for a Leading Edge Impingement System

International Journal of Turbomachinery Propulsion and Power ◽

10.3390/ijtpp3040023 ◽

2018 ◽

Vol 3 (4) ◽

pp. 23

Author(s):

Robert Pearce ◽

Peter Ireland ◽

Ed Dane ◽

Janendra Telisinghe

Keyword(s):

Heat Transfer ◽

Experimental Data ◽

Turbine Blades ◽

Leading Edge ◽

Reynolds Numbers ◽

High Heat ◽

Navier Stokes ◽

Spatially Resolved ◽

Computational Fluid Dynamics Simulations ◽

Dynamics Simulations

Leading edge impingement systems are increasingly being used for high pressure turbine blades in gas turbine engines, in regions where very high heat loads are encountered. The flow structure in such systems can be very complex and high resolution experimental data is required for engine-realistic systems to enable code validation and optimal design. This paper presents spatially resolved heat transfer distributions for an engine-realistic impingement system for multiple different hole geometries, with jet Reynolds numbers in the range of 13,000–22,000. Following this, Reynolds-averaged Navier-Stokes computational fluid dynamics simulations are compared to the experimental data. The experimental results show variation in heat transfer distributions for different geometries, however average levels are primarily dependent on jet Reynolds number. The computational simulations match the shape of the distributions well however with a consistent over-prediction of around 10% in heat transfer levels.

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Cold-Weather Cast-in-Place Segmental Construction for Long-Span Bridges

Transportation Research Record Journal of the Transportation Research Board ◽

10.3141/1712-19 ◽

2000 ◽

Vol 1712 (1) ◽

pp. 157-163

Author(s):

Christopher J. Burgess

Keyword(s):

Saint Paul ◽

Cold Weather ◽

Monitoring Method ◽

Box Girder ◽

Long Span Bridges ◽

Long Span ◽

Batch Plant ◽

Reinforced Plastic ◽

Post Tensioning ◽

C 50

An innovative heating and monitoring method was developed and used for wintertime casting of the Wabasha Street Bridge in Saint Paul, Minnesota. The bridge’s twin 384-m (1,260-ft) box-girder structures slope 5 percent from atop Saint Paul’s bluffs on the Mississippi River’s north side down to the lower portion of Saint Paul. Each box girder is composed of two 122-m-long (400-ft-long) center spans and two 70-m (230-ft) approach spans. The deck width of 14.54 m (47 ft 8 in.) contains two 3.66-m (12-ft) travel lanes, two shoulders of 0.92 m (3 ft) and 1.83 m (6 ft) with a 3.36-m (11-ft) sidewalk, and 1.11 m (3 ft 8 in.) to account for the barriers. The superstructure consists of 4.88-m (16-ft) typical-length segments that are 6.10 m (20 ft) deep over the piers and 2.44 m (8 ft) deep at midspan and the abutments. The bridge was constructed in balanced cantilever fashion with form travelers. The contractor, the local concrete supplier, the city, and the Minnesota Department of Transportation worked together to develop an innovative mix that would withstand the frigid temperatures and also achieve 24 115 kPa (3,500 lb/in.2) compressive strength in less than 24 h to allow the stressing of the post-tensioning. To insulate and protect the curing concrete, reinforced plastic enclosures surrounding the form travelers housed three 316 761-kJ (300,000-Btu) propane heaters. A layer of plastic and a double layer of insulating blankets covered the top slab. Thermocouples in the segments provided temperature readings, which the contractor used to monitor the effectiveness of the cold-weather procedures. The forms, reinforcing steel, and previous concrete were heated above 10°C (50°F) by using plastic enclosures, propane heaters, and insulating blankets. The concrete arrived from the batch plant at approximately 21°C (70°F) and was still above 13°C (55°F) when it was pumped into the segments. Multiple thermocouples indicated that the top slab cured above 38°C (100°F) for several days, whereas the bottom slab and webs were about 11°C warmer. The contractor ran the propane heaters for 5 days after each pour or until the segments reached a 28-day strength of 41,340 kPa (6,000 lb/in.2). The segments reached the required 24 115 kPa (3,500 lb/in.2) strength for post-tensioning on the day after each pour, including pours made on days as cold as −28°C (−19°F). Only 3 working days were lost because of the cold, and the bridge was completed on time. The method of heating and protection used at the Wabasha Street Bridge proved that the segmental cast-in-place construction method is a viable option in cold-weather climates on major long-span bridges.

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